THE FORMS OF THE SOCIAL LIFE THAT OCCUR IN INSECTS

Insects are small living animals which have four wings and usually wings, for example ants, butterflies, and flies etc. Insects are invertebrate animals in the class insecta. Their adult bodies are divided into head, thorax and abdomen. These animals have three pairs of segmented legs which are attached thorax and one pair of antennae. Insect that are fall under subclass Pterygota have two pairs of the wings and the insects fall under the subclass Apterygota does not have wings. Insects are ecologically important as other animals such as herbivores, predators, parasites and scavengers. They are also considering being the most successful group of organisms on the Earth.


Insects have a complex life cycle consists of many small part transformation known as metamorphoses. Insects have different body shapes, functions and behaviours at each stage of metamorphoses. Butterflies, moths and true flies are the insects that have more complicated life cycle which also have four stage including eggs, larva, pupa and adult. Spring tails and bugs are the insects that have less complex development which include eggs, nymp and adult stages. Most of the insects are non-social and some species have developed complex social behaviours, they are living together and caring for eggs. The young once are the offspring of a single female known as the queen and this system is common in insects such as bees, wasps, ants and termites.


The life of insects is in danger in many ways. They may be eaten by other insects, birds, and some other animals etc. Human being may kill them by crushing, burning or poisoning them. The parasites which are the animals, who feed on living animals, may kill and eat them; and disease may also kill them. Insects may also killed by cold weather. The other things is that a dry spell may cause the plant the shrink, dries up and dies and this means that insects that depend on that plant may suffer and end up dieing. Even if the insects and other species can survive these dangers, it means that there will be running out of the food supply and it also means that they will die because of the shortage of their food.


An insects developed many ways of their life survival. They adapted themselves to a living conditions and developed many ways to get away from their enemies. Most of insects spend a lot of time on eating and reproducing and everything they do is related to those two activities. Insects can also communicate to each other and they can get the message by touching and smelling, for example, the queen releases airborn chemicals called pheromones and foreign insects can be attact by this chemicals. Social insects also share information about food, for example, ants lay scent trails that lead to feeding site and bees returning to the hive dance that shows the direction of the food sources. So with this information, other insects can find sources of food away from that area.


Communication is an important for mating and defence among the nonsocial insects. Insects such as grasshoppers, crickets and cicadas produce their sound which can attract mating parterners and this process is called stridulation. Stridulation involves rubbing one body part against another to produce sound and cicadas produce sound by clicking a taut membrane. Their ears are called tympana and they use them to detecting one another’s song. Some insects use their antennae to hear sound made by other species members. Mosquitoes use their featherlike antennae to hear the sound of the female wing-beats and water strides use their legs to attract.


References:

Wikipedia contributors. Arthropod [internet].wikipedia, The Free Encyclopaedia, 2006, May 8, 3:40 UCT [cited 2006 May 6]. Available from: http://en.wikipedia.org.wiki/Arthropod

Wikipedia contributors. Insects [internet]. Wikipedia, The Free Encyclopaedia, 2006, May 8, 3:40 UCT [cited 2006 May 6]. Available from: http://en.wikipedia.org.wiki/insects



Lizzy Maluleke
CSIR PTA
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Cell number 072 351 8488
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THE FIRST PLANTS AND ANIMALS EVOLVED AND BECAME DEPENDANT ON EACH OTHER

Plants take carbon dioxide and release oxygen in the process of photosynthesis, animals inhale oxygen and exhale carbon dioxide in the process of breathing. Plants play an important role in the nature cycle. Without plants there would be no life on earth. Plants are the only organism that can make their own food. We breathe oxygen from plants. The quality of air is influenced by plants because plants can stop the movements of dust and pollutants through the intake of carbon dioxide plants reduce the greenhouse effect which comes from the burning of fossils fuels.

The first animals to evolve are called multicelled Eukaryotic animals. These evolved from colonies of single celled organisms. During this time animals were small and simple but evolved into all larger and more complex animals. The first fish evolved and the oceans were dominated by different types of invertebrates.

Single celled organisms developed during 2,5 million years ago. During this time the earth and atmosphere were stable enough to support primitive life. The first plants to evolve were Blue-green Algae. Blue-Green Algae used sunlight and water to make food, and in the process, created oxygen. Blue-Green Algae grew in the earth seas and they began to fill the atmosphere with oxygen which made it possible for other organism to develop. Plants are the only organisms that can make their own food but animals can not makable to make their own food and they depend directly or indirectly on plants for their supply of food. All animals and the foods they eat can be traced back to plants.

Plants and animals are made by many types of cells. Plants have thick and rigid walls that consist of cellulose where as animal cells do not have these materials. Cellulose enables plants to stand upright with out an internal or external skeleton. Plants also depend on insects for distribution of the male reproductive cells. We breathe oxygen from the plants, through the process of photosynthesis. Plants absorb energy from the sun, and carbon dioxide from the air and water from the soil. Animals take part in this cycle through respiration. Respiration is the process where oxygen is used by organisms to release energy.

Plants make the Earth’s atmosphere livable for humans and animals by changing carbon dioxide into oxygen. Plants are used by both humans and animals because we can use plants as food, plants as medicine, or plants as decoration. Leaves are the main food makers for plants. Because they capture energy from sunlight, and turn water and carbon dioxide into sugar and starch. One can undertake research science on plants, how plants grow, why they change colour, and one can also learn about different plants and ecosystems around the world, and how they are affected by human habitats. .

Plants play an important role with regard goods; they provide fibres and these in turns provide clothing. Wood is also used to build our houses, and burnt to keep us warm and cook our food. It plays important part in the quality of water because they hold the soil in place and control stream flow and filter sediments from water. Plants also prevent erosion.
They also play an important role by role by role by providing the necessary habitat for wildlife and fish populations. The amount of sunlight and rainfall are limiting factors for both plants and animals because both affect plant growth.

REFERENCE
Kazlew. A.M. 2002,plants, (land plants). [Internet]. 2006 may 08, 14:00 [Cited 2006 May 08]. Available from:http://www.palaeos.com/Plants/default.htm

Wikipedia contributors. Segmentation [internet].Wikipidia, the free encyclopedia; 2006 march 24, 11:10 UTC [cited 2006 May 08] available from:http://en.wikipedia.org/wiki/Segmentation_(biology)

Linette Netshiheni

CSIR

Pretoria

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Cell: 0820446442

Tell: 012 841 2133

Fax: 012 842 3676

tnetshiheni@csir.co.za

Weblog: http://tnetshiheni-linette.blogspot.com/

THE FORM OF SOCIAL LIFE THAT OCCUR IN INSECTS

Insects are small animals around us; they are invertebrate animals of the class insecta, the largest and most widely distributed group of animals within the phylum Arthropoda. An insect consists of six legs and the three body parts, namely a head, a thorax and an abdomen (8).


The insects were probably the first animals to fly. Most of the insects have one or two or even three pairs of wings which they developed millions of years before bats and birds. They are known to be excellent fliers, they fly in big groups and they like doing trick flying. There are over 800,000 different kinds of insects that are known and being discovered daily. They live almost everywhere in the world and they are very adaptable. Many insects such as butterflies and moths go through the four stages of growing. They are firstly an egg to being like a worm (larva) then goes to pupa where they take a nap. Finally the new insect will break out of their pupa and therefore, an adult insect (8, 3).


The insects are categorized into three different groups, namely:Holometabolous (the complete metamorphosis), the pupae is formed in this stage, and the examples of these insects are beetles, flies, bees, lacewings, butterflies, ants and caddis flies. Hemimetabolous (the incomplete metamorphosis) there is no pupae in this stage and the examples of these insects are crickets, true bugs, termites, grasshoppers and cockroaches. Ametabolous is without the metamorphosis, example is silverfish (2).


There are about two subclass of the class insecta namely: Apterygota and Pterygota, and they are further divided into the orders. "The Aptergota into microcoryphia known as dragonflies, damselflies and Zygentoma known as silverfish and firebrats while the subclass Pterygota is divided into twenty one orders namely Ephemeroptera known as mayflies, shadflies. Odonata known as dragonflies and damselflies. Dictyoptera are known as cockroaches and mantids. Isopteran are known as termites and white ants. Athoptera are known as grasshoppers, locusts, katydids and crickets. Phasmida are known as stick and leaf insects. Dermaptera is known as earwings. Grylloblattodea are known as rock crawlers, ice insects. Plecoptera is known as thrips. Psocoptera is known as scorpion flies. Trichopterais is known as caddisflies. Coleopteran is known as beetles. Neuropteran are known as lacewings, mantispids and ant lions, and the Hymenoptera known as bees, wasps and ants” (6).


However, insects are known to be excellent fliers but there are still some of the insects without wings. These types of insects are jumping insects, for example: silverfish, fibre brats, fleas, etc. The true flies are the most known excellent flier. The mantids are known to be the excellent pest control, because they eat other insects in the garden and their large species can also eat frogs, lizards and even hummingbird. The fleas depend on the blood of their hosts like dogs, cats, birds and humans to survive (6).


The insects fly for couples of reasons, "some fly to survive, others fly in order to find insects that they can mate with, while others fly to get better foods, all in all they fly to escape they predators. There are some of the insects that fly during the day, like butterflies while some like moths’ flies at night. There are also seasonal insects, butterflies comes out in summer and spring. During winter the insects migrate to escape the killing temperature, while others are hibernating as larvae, others as nymphs, others as eggs, others as pupae and others hibernate as adults. Insects can survive the cold condition easily only when the temperature is stable. Many insects can get shelter and nourishment through the winter in the variety of micro – habits” (1, 8).


References:

1. [http://library.thinkquest.org/5767/:butterF.htm, accessed on 06/05/2006, 09:00]

2. Using live Insect (1997) The University of Arizona [http://insected.arizona.edu/insectinfo.htm, accessed on 06/05/2006, 09:30].

3. [http://library.thinkquest.org/5767, accessed on 06/05/2006, 10:00].

4. [http://www.kidport.com/RefLib/science/Animals/Insects.htm, accessed on 06/05/2006, 10:20].

5. The k8 Aeronautics Internet Textbook site, [http://wings.avkids.com/Book/Animals/Intermediate/insects.01.html, accessed on 06/05/2006, 11:40].

6. The family tree, [http://www.insecta.com/insecta/tree.htm, accessed on 06/05/2006, 12:00].

7. [http://www.si.edu/resource/faq/nmnh/buginfo/winter.htm, accessed on 06/05/2006, 12:30].

8. Wikipedia contributor, insect [internet]. Wikipedia, the free encyclopaedia, 06/05/2006, 12:40 PTA cited, available http://en.wikipedia.org/wiki/Insects].



Ms Evelyn Maleka
CILLA CSIR
P.O. Box 395
Pretoria,
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Fax: 012 842 7024.
Email: emaleka@csir.co.za
http://malekaevelyn.blogspot.com/

HOW THE FIRST PLANTS AND ANIMALS EVOLVED TO BECOME DEPENDANT ON EACH OTHER

Scientists believe that nearly 2.5 billion years ago after the big bang some 13 to 14 billion years ago the surface of the earth and the evolution of the atmosphere became stable in order to support the early life. Therefore, organisms with a single cell started to develop in the sea which covers the planet, earth. It is also said that the sea has been formed by the accumulation of water vapour and carbon dioxide yielded by the volcanic eruptions. The first evolution of plant started with a single cell organism known as the blue green algae. On the other side the first animal to evolve is thought to be from a multi cellular organism. In other words this means that according to the scientists life has began in the sea.


When the blue green algae started to grow in the seas of the earth, they produce oxygen which then spread through around the atmosphere we know today. The availability of ''oxygen in our atmosphere made it easier for the other organisms to develop on the earth'' (Mcland, 2004: 2). That is why plants are called producers, because they are the once that brought life on the earth by being able to produce their own food during the process of photosynthesis.


During the process of photosynthesis, the blue-green algae use energy from the sunlight, carbon dioxide from the atmosphere, water and mineral from the soil. Mcland (2004) further says that at the same time when they photosynthesize, they release oxygen and water which are useful for life of other organisms on the earth. Animals and other organisms use the produced oxygen and release carbon dioxide which is also used by plants during the process of photosynthesis.


The first animal to evolve is thought to be eukaryotic animal. The information has been found by studying the fossils of multi-cellular eukaryotic animal. It is further explained by saying that the multi-cellular organisms underwent evolution from a single cell organism. Even though the first animals were very small, but they did manage to evolve into all other large and complex animals that we see on the earth today. The first animal were called eukaryotic because they possess nucleus in their cells as opposed to prokaryotic animals which they do not possess nucleus in their cells. These first animals are called consumers, because they ''depend on plants for their food'' (Wikipedia contributors). Therefore animals depend on plants for their food.


In conclusion, plants especially the blue green algae are thought to be the first plants to evolve on earth. They are also termed producers because they use energy from the sun, carbon dioxide and water to produce their own food during the process of photosynthesis. On the other side the first animal to evolve is thought to have evolved from a multi-cellular eukaryotic animal in the colonies of a single cell organism. Therefore animals and other organisms depend on plants for food because they are incapable of manufacturing their own food. Plants are also first in the food chain because they have the ability to manufacture their own food.


References:

McLand, E. 2004. The quite Evolution of Trees. [Online]. Available from:
http://www.ecology.com/feature-stories/quiet-evolution-of-trees/index.htm [2004, February 12]

Wikipedia contributors. Segmentation [Internet]. Wikipedia, The Free Encyclopaedia; 2006 March 24, 13:04 UTC [cited 2006 May 08]. Available from: http://en.wikipedia.org/wiki/Segmentation_(biology)

Wikipedia contributors. Evolution [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 08, 06: 45 UTC [cited 2006 May 08]. Available from: http://en.wikipedia.org/wiki/Evolution


Peter Muvhali
CSIR PTA
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Tell no: 012 8142133
Fax : 012 8423676
E-mail: smuvhali@csir.co.za

URL: http://blogsoccer-peter.blogspot.com/

DESCRIPTION OF THE FORMS OF SOCIAL LIFE IN INSECTS

Insects are invertebrates. Invertebrates are insects without backbone. Insects are thought to have a variety of social behaviours. Some of the social behaviours which are found in insects include living together in ''large groups, communication, sharing of the food, feeding and protecting the young insects and the eggs'' (Wikipedia contributors, 2006). The above mentioned behaviours are usually found in bees, ants, wasps and termites. The permanent living together of the insects is known as the colonies. This means that by living together, they also work for the survival.


In insects, ''females are usually the once who are responsible in the finding of the social colonies'' (Lang, 2006: 1). The single female insect which is usually the founder of the social colony is termed the queen. It is termed the queen because after mating is the one which builds the nests where it will start with the laying of the eggs. After the young insects have been raised, they take the responsibilities of the queen, so that the queen may continue with her concentration on her reproduction.


Unlike in other insects, in the other colonies of the honey bees, there are three divisions. They are divided into the workers, queen and drones. Male honey bees are termed drones, while their female counterparts are termed sterile. Lang (2006: 2) further says that ants and termites are also divided into two groups which is soldiers and workers. Workers and soldiers have different functions to perform. The function of the soldiers is usually to defend the habitat or the nest. While on the other side the function of the workers is to store food which has already been gathered and the release of the sugar in case where the food is hard to be found.


One of the most significance of the social behaviour of the insects is communication. Insects do communicate. It is said that during darkness and in the crowd while they are in the nest, touch and smell are the most usefully used in conveying the messages. During the sending of the messages, the ''queen as the mother of the nest release pheromones which is a chemical used to stimulate other members of the colony to act as unit among themselves'' (Wikipedia contributors, 2006). The formation of the cohesion among the insects also helps them when the foreign insects get into their nest, because it will be attacked immediately after entering the nest.


As sharing seem unlikely human beings, in insects sharing in significance. This is because insects usually share information about the food. This is done by workers when they enter and leave the nest. By doing so, workers make contact to be able to find where the other insects have gathered their food. In ants, tracks that lead to the place where the food is available are made. In honey bees, the direction of where the food is found is made by making unusual dances to show others the direction where the food has been found.


In conclusion one can say that, even though there is a huge different between the insects and human beings when coming to the social behaviour, but there is a slight similarities such as the taking care of the nest by the queen. Taking care of the nest by the queen is similar to the care taken by the female in homes.

References:


Wikipedia contributors. Insects [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 8, 12:27 UCT [cited 2006 May 6]. Available from: http://en.wikipedia.org/wiki/Insects

Wikipedia contributors. Arthropod [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 3, 12: 47 UCT [cited 2006 May 6]. Available from: http://en.wikipedia.org/wiki/Arthropod

Lang, S. S. 2006. Social behaviour of sweet bees evolved with Earth's a mere 20million years ago, Cornell study finds. [Online]. Available from: http://www.news.cornell.edu/stories/March06/social.bees.evolution.ssl.html


Peter Muvhali
CSIR PTA
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weblog: http://blogsoccer-peter.blogspot.com/

THE VARIATION IN SHELL STRUCTURE THAT HAVE OCCURRED IN THE PHYLUM MOLLUSCA

The largest phyla in all phylum are called phylum mollusca. It is large in number of species and in both size of species. The structure of phylum mollusca shell is difficult. Phylum mollusca consist of two layers, which are the outer and inner layers. The inner layers have calcium carbonate and the outer layers consist of peristracum. This periostracum has organic chemicals and the chemical that occurred in the periostracum is referred as conchion. Calcareous shell is protected by this periostracum. Periostracum plays an important role in the formation of microscopic shell. The calcareous shell structure that occurred in the inner layers is very complex and variable. The calcium carbonate that occurred in the outer layer has crystals. Those crystals are laid down in an organic matrix which is deposited as a calcite. Even though the calcite is the main shell in oysters.

The body of mollusca is bilaterally symmetrical, and its body plan is flexible. Phylum mollusca consist of body mass. The structures of phylum mollusca are unique. Mantle and Redula are the structure of phylum mollusca. Redula is like a toothed tongue and the mantle is a flat. The body of phylum mollusca is divided into six classes. That is, Monoplacophora, Polyplacophora, Gastropods, Pelecypoda, Cephalopods and Scaphopoda. The dominant classes in phylum mollusca are Gastropod, Cephalopods and Pelecypods. Now we can focus on members of each of these classes to get their similarities and differences and the variation in shell structure.

Gastropods

Snails are good examples of this class. Gastropods are like the ancestors of mollusca than other classes. They differ from primitive ancestors, because they have enlarged head. Gastropods are marine. The foot of Gastropods are broad flat organ. Gastropods are most successful group of phylum mollusca. It is large due to the wider range of habit. The class gastropods are large, not only in terms of number of species. Gastropods have well developed head. This head includes tentacles, eyes and mouth. Its foot is fattened.

Pelecypoda

Members of this class are claims, mussels, scallops and bivalves. Bivalves do not appear much in snails. It also found in every marine environment. Most of bivalves are suspension feeders, in small organism and organic particles from water. Bivalves are sedentary. Bivalves have developed from primitive molluscan form. It has not Redula. The body of bivalves is dominated by mantle cavity and the head is suppressed. The majority of bivalves are cilliary feeder with plate-like food. Bivalves have gills which serve as a developing young and serves as a food sorting organ and respiration.

Cephalopods

Members of this class are squids and octopus. Cephalopods are invertebrates. It consists of external shell and internal hard shell. The relationship between Cephalopods and mollusca is not obvious. The head and foot of Cephalopods are combined to form cephalised frontal end, because of these process the loss of shell and reduction will occur.

Aplacophora

Aplacophora has no outer shell. All Aplacophora have mantle cavity. Aplacophora are found throughout the oceans. Its habitat is fully marine salt water. Aplacophora are small and cylindrical. All Aplacophora have simple mantle cavity.

Monoplacophora

Monoplacophora are mainly found in very deep water. It is very thin and fragile. Members of this class have a single, cap shaped shell which is similar to a limpet. The shell of monoplacophora is small and range from 3 to 30mm diameter.

Scaphopoda

The wider end of the shell was head and foot. Its shell is usually four layers which are used for identification. It has a short head, conical projection with a mouth. The shell surrounds as large mantle cavity. It has no ctenidia and gas exchange is through the mantle surface. The shell is open at both ends. The shell is curved, tubular and shaped like an elephant tusk. Its average is 3 to 6cm long but range from 4mm to 15cm.

REFERENCES

Mulcrone, S.R, 2005.Animal Diversity. Web. [Online] Available from:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Aplacophora.html
[2006 May 08, 10:17]

Wikipedia contributors. Coordinated Universal Time [Internet]. Wikipedia, Mollusca, The free Encyclopedia; 2006 May 05, 10:15 UCT [Cited 2006 May 08] Available from:http://en.wikipedia.org/wiki/Phylum

Linette Netshiheni
CSIR
Pretoria
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Cell: 0820446442
Tell: 012 841 2133
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tnetshiheni@csir.co.za
Weblog: http://tnetshiheni-linette.blogspot.com/

FOSSILISATION AS A PROCESS AND ITS SIGNIFICANCE IN INTERPRETATION OF EVOLUTIONARY EVENTS

The term fossilisation refers to the deposit of inorganic processes which allow the remains of a past living creature to be after its death. This word is derived from the Latin word meaning dug up. On the beginning of ancient Greeks it was used to describe different objects or materials found underneath the ground or found lying on the surface of the earth including mineral ores, rocks, stone implements and organic remains.

Fossils are formed when a living organism dies and the body or part of the body is preserved in a different way but usually by being buried rapidly in sediments. Burial prevents destruction of organisms by scavengers, bacteria or weathering. In most cases burial can occur in different places like on the bottom of the sea, in rivers or in Lakes. Shells bones, teeth, husk and skeleton are the only hard parts which are preserved usually and they are can survive even if subjected to traumas such as impact fracture, disintegration or dispersal caused by atmospheric phenomena . In some instances soft parts such as mammoths are also preserved but it is hard for them to survive because they are vulnerable to predation and decomposition.

The importance of fossils is in interpreting the evolutionary events, like in the case of dinosaurs. If it was not of fossils the generation of today would not even have a clue on how it use to look like. Fossilisation as a process can only take place when certain conditions are present. This process depends on the chemistry of an environment and on the biochemical make-up of the organisms. There are different processes through which fossils can be preserved:

Pertrification is the crystallization of minerals inside cells. One of the best known forms of "Pertrification is silicification, a process in which silica-fluids enter the plant’s cell and crystallize, making the cells appear to have turned to stone. Pertrification can also occur in animals when minerals such as calcite or silica fill the pores and cavities of fossil shells and bones.
Carbonization plants are mostly fossilised through this process. The mobile oils in the plant’s organic matter are leached out and the remaining matter is reduced to a carbon film. Plants have an inner structure of rigid organic walls that maybe preserved in this manner, revealing the framework of the original cells. Animal soft tissue has a less rigid cellular structure and is rarely preserved through carbonisation.

Recrystallization animal shells are composed of mineral aragonite, a form of calcium carbonate that breaks down over millions of years to form the more stable mineral calcite. This method of preservation destroys the microscopic details of the shell but does not change the overall shape.
Mummification may occur in hot arid climates which can dehydrate organisms before their soft tissue are fully decayed. The skin itself is preserved for only a short time but the impressions of the skin in the surrounding sediment turns to rock"

There are other different methods for preserving but they all perform different functions. Everything which happened in the past is discovered through fossilisation and it is compared to the present evidence if such species still exist.

Reference


1.Wikipedia contributors. Dinosaurs [Internet] Wikipedia, The free encyclopedia;2006 May 16; 16:20 UTC [Cited 2006 May 20]. Available From:
http://www.museum.vic.gov.au/dinosaurs/sci-form.html

2. Wkipedia contributors. Paleontologia [Internet] Wikipedia, The free encyclopedia; 2006 May 16; 16:21 UTC [Cited 2006 May 02]. Available From:
http://www.musei.unina.it/Paleontologia/eng/3.2.4.1.htm

3. Wikipedia contributors. Fossil [Internet] Wikipedia, The free encyclopedia; 2006 May 16; 16:21UTC [Cited 2006 May 02]. Available From:
http://palaeo.gly.bris.ac.uk/communication/harrison/fossil.html

Dianah Nangammbi
Cilla CSIR
P.O Box 395
Pretoria
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Email: dnangammbi@csir.co.za
Tel: +27 12 841 2133
Cell: +27 73 121 3589
My blogger url: http://wwwdianah.blogspot.com/

VARIATIONS IN SHELL STRUCTURE THAT HAVE OCCURRED IN THE PHYLUMMOLLUSCA

Molluscs have evolved in the world 600 million years ago during the Ordovician period. “The first molluscs were simple warm like having segments” [1] and it use crawling mode of locomotion. During the Ordovician period seven class molluscs which are present to day were present, they only underwent modification because of their vulnerability to predators. Molluscs are composed by soft bodies, because of predators they underwent modification to develop the hard shell to protect themselves.

Because of the soft bodies that molluscs have, “they produce an external skeleton known as exoskeleton” [1]. It is a hard part that cover the back of molluscs, it also serve as the protective organ, because is not simple for predators to break it. This exoskeleton or shell is formed by calcium carbonate (CaCO3).”In most of the molluscs there is flesh mantle that secretes, modifies and line the shell with mucous” [1] for better locomotion and for protection when there is a predator it allows the body to flip inside the shell smoothly.

Adaptations of the molluscs determine the difference of shell structure to occur in molluscs, these determined by the environment that they are living in. some molluscs chose to live in terrestrial, while other chose to live in the aquatic environment. This adaptation bring difference to the shell structure, some grow large while other looses their shell completely.

Molluscs which have niche in the aquatic environment have different shell structure to the molluscs that live in the terrestrial. Most of the molluscs that have habitant on the ocean they have dome shape shell, while the terrestrial molluscs have the spiral shell structure. This modification and shape of shell structure depend on the environment and the capability of movement, the shape of the shell can also determine the mode as the weight that they have can weigh more and push the molluscs to move in the other way.

The shape of the molluscs that are found in the ocean, they have a dome shape, which is formed by plates. There are eight plates which overlap each other in a very tight way to protect the molluscs from violet serge of ocean waves. Primitive molluscs such as polyplacophora have under gone modification and adopt this type of shell structure, dome shape. It has habitant in shallow water in the ocean.

While those that found on the bottom of the water or ocean have adopted different modification of shell structure. Class Monoplcophora which are found in the deep water have modification on their shell structure, which enables them to walk on the ground level of the sea. They have bilateral shell with a disk shape valve less than 25mm, this shell structure is fragile and thin. The body of molluscs of class monoplcophora does not have segment, but the shell structure develop coiled chambers which is covered with Horney sheath.

Other molluscs develop cyndrical tube which opens at the both end, which resemble the tusk of an elephant. It is elongated, symmetrical and tubular, this type of shell found on the molluscs that found burrowing in the mud, they use their shell to create the burrowing niche.

While other class of molluscs such as Aplocophora do not have shells and there is no fossils that indicate that they were having one. The flesh mantle that they have does not produce shell, but their modification tends to influence “flesh mantle to produces calcareous spicules”. [1] These spicules protect them from predators as it become less palatable.

In all molluscs gastropod underwent a very important modification in the evolutionary part, this influence the change in shell structure. Before its shell was symmetrical coiled like garden horse, but because of modification it change to central axis were coils are laid down, in order to balance out weight of the shell. This modification that gastropod underwent was influence by the habitant they occupy they live in both environment terrestrial and aquatic.

In nutshell the importance of the shell in all molluscs is to give protection to the molluscs as they are vulnerable to predators and their body are soft in such away that it cannot stand the disturbance that can involve when it moves .it also helps them to adapt different environment. Molluscs that live in terrestrial have hard shell that protects them from radiation and predators. While those that found in the aquatic have soft shell that protect them from ocean wave.

Today because of modification in shell structure that molluscs have it allows them to occupy almost all environments. The different that the shell structure has is the one that identify the habitant of the molluscs.

References

1. Bourquin.A.2000. The Phylum Mollusc: [internet] [cited 2006-May-4] Available from: http://www.manandmollusc.net/advanced_introduction/advanced_intro_printable.html

2. Wikipedia contributors. Aplacopra [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 20, 05:55 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Aplacophora


3. Wikipedia contributors. Polyplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 12, 14:07 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Polyplacophora

4. Wikipedia contributors. Monoplcophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 21, 01:25 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Monoplacophora

6. Wikipedia contributors. Scaphopoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 23, 12:22 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Scaphopoda

7. Wikipedia contributors. Gastropoda [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 20, 06:36 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Gastropoda

Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://www.emuanalo.blogspot.com

DESCRIBE THE PROCESS OF FOSSILIZATION AND ITS SIGNIFICANCE IN THE INTERPRETATION OF EVOLUTIONARY EVENTS.

Fossilization is the process that involves non-living, which enable the remains of formerly living creature to be preserved after its death and following burial under sediment. This process only takes place in present of certain conditions or factors and these factors play a role in preserving the fossils. The process depends on chemistry of the environment and the biochemical makeup of the organism. Therefore because different organisms are made of different bio-chemical makeup not all organisms may be fossilised thus few in many organisms are fossilised.

The hard parts of dead animals are usually preserved as fossils; this includes shells, bones and teeth. The process begins with the dead of plants and animals. After they died, they are buried on the ground. The soft body parts decay and rot after death and the process is carried out by bacteria and scavengers. Different processes are involved in fossilization of plants and recrystalization. The body is buried under more and more layers of sediments overtime. Hard body parts are replaced by new minerals such as calcite or quartz or pyrite and this process is known as petrification. Sediments are further compacted further again by the weight of rocks above. At later stage the rocks are pushed up to form mountains fossils may be seen at later stage after million of years when the rocks are worn down to reveal the fossil.

Fossils are important as they allow the scientist called palaeontologists to find more information about biological organisms that existed in a period of time that predates our own. Knowing something about the kind of ancient life and the environment that existed long ago can tell us how Life become accustomed but also how the climate changes. Therefore by knowing something about the past we may be able to make a more informed prediction about what could happen in the future.

Fossils can also just tell us great stories about what was happening millions of years ago. For example fossilized footprints of a heard of dinosaurs running from danger or how they may have cared for their young. Discoveries of fossilised nests and eggs can tell us how they may have lived. The fossils are also important to tell more about the sizes and structure of organisms that existed in a period of time. These also help to understand the species that evolved longer than the other.

Currently, Fossils are also potentially economically. Quite big business, either directly by people finding examples and selling them or the industries like movies makes millions of dollars based on stories that come from fossil discoveries.


References

1. Fossilization, [internet] [cited 2006 may 5]. Available from:
http://www.museum.vic.gov.au/dinosaurs/sci-form.html

2. Fossilization, [internet] [cited 2006 may 5]. Available from:
http://www.musei.unina.it/Paleontologia/eng/3.2.4.1.htm

Mr Lufuno Mukwevho
Cilla CSIR Pretoria
P.O. Box 395
Pretoria
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Tel: (012) 841 2133
Fax: 012 842 7024
cell: 0723175626
email: lmukwevho@csir.co.za
my bloger url: http://mukwevholufuno.blogspot.com

THE PROCESS OF FOSSILIZATION AND THE IT’S SIGNIFICANCE IN THE INTERPRETATION OF THE EVOLUTIONARY EVENTS.

Fossils refer to the remains of plants and animals that existed many or long time ago and it is mostly occurring in sedimentary rocks and the process of fossilization occurs when living organisms such as animals and plants dies. This process of fossilization mostly occurs near the river where there is a lot of sand. Fossilization mostly occurs on big organisms that have hard body parts such as bones, teeth, clews and shells. It is impossible for small animals to be fossilised because they have a soft bodies and they do not live for the long time, so they can became extinct.


When the animals died, their meat is eaten by their enemy or predators and leaves their bones. "These bones will be left untouched, and when the wind blows the sand and sediments, these bones will be covered and place underground. The organism must be covered by sediment soon after they died or decaying process and the sediments will continue cover up the bones until they are hidden far underneath the ground. After they have been covered with sediment they become solid and they will be covered into rock and organic remains replaced with a minerals and it is called diagenesis form" (Wikipedia contributors, 2006).


During the process of fossilization "minerals, calciums and hydroxyapatite found in the bones replace by the minerals that are found in the sand and after many years, and there will be a lack of an organic materials in the bones because they will turn to solid rock and end up to being a fossils. There are two types of fossils, namely: organic fossils which were once part of living organism and trace fossils which are the trackways, burrows, footprints, eggshells, nests and worms holes" (Wikipedia contributors, 2006).


The fossils of small animals such as insects, spider, and small lizards can be found in "the mud stone or sandstone and psedofossills are produced by natural occurring in the geological process and same of these fossils such as dendrites are formed by naturally occurring in the rock that filled up with the percolated minerals. Other examples of the psedofossils are kidney ore and moss agaster" (Wikipedia contributors, 2006).


The reef-building corals fossils show that "the rocks were deposited in warm and were found in the tropical seas where sunlight can pass through the water to reach the their photosynthesising algae within their cells. Fossils may be formed close to the edge of the body of water. The Koonwarra fossil includes fossilised fish, plants, insects spiders and bird feathers. These fossils show that the deposit was formed in the dip part of the large freshwater lake because the insets are living in cool mountain streams and in lakes. These insects were not transported far after their death"(Wikipedia contributors, 2006).


Most of the fossils are found in the sedimentary rocks that have been formed by the consolidation of the soft sedimentary such as sand and mud. Fossils which are found in igneous rocks are hidden from a molten state or in the metamorphic rocks that have undergone intense pressure and heat. The fossils occur in sediments such as rocks, and incorporated as an integral part of the rock formation. Unconsolidated sediments such as sand or muds are good for burial. The other thing is that fossilization is the process of the hard part of the skeletons and shells etc and these were fossilized under high favourable conditions.


References:

1.Wikipedia contributors. Fossilization [internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 13:36 UCT [cited 2006 May 8] available from:
http://en.wikipedia.org/wiki/fossils

2. Fossilisation [Internet ] Wikipedia [cited 2006 May 03] Availabe from: http://www.museum.vic.gov.dinosaurs/sci-form.html



Lizzy Maluleke
CSIR PTA
0001
Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
Weblog: http://mmaluleke.blogspot.com

THE PROCESS OF FOSSILIZATION AND ITS SIGNIFICANCE IN THE INTERPRETATION OF EVOLUTIONARY EVENTS.

Fossilisation can be referred as the set of inorganic processes which allow the remains of formerly living organisms to be preserved after its death and buried under sediment. It happen only in dead organisms, usually the hard parts can be preserved (bones, husk, shell, etc), because they can survive the alteration and disintegration or decomposition caused by atmosphere phenomena while Soft parts are rare to be fossilised this because they are vulnerable to predator and decomposition.

This process of preservation is influenced by natural processes (weathering, floods and volcanic eruption) which bury dead organisms in the surface. Some natural process cause death of the species and some of the process bury them in sediments. Volcanic eruption can cause death to many species and it can bury them on its larva, while erosion erodes all the dead particles and deposited them with other material to form sediments. Weathering which cause breaking down of rocks bury dead organisms in the particles and form sediment or rock.

Environmental condition also plays a part in perseveration of fossils this occur in the maintenance of the morphological structure of the species, if not altered by destructive agent they can keep their morphological structure. Fossilisation that happen in terrestrial environment like marine or fluvial environment are well preserved this because depositing agents act more quickly in marine environments than degrading ones. Morphological structure can be disturbed by physical changes that may involve, like flattened or distorted as sediments is hardened into rock.

Factor that influence the preservation of fossils are:

Carbonization which is known for plants where the organic matter are leached out and reduced to carbon film and the rigid organic walls are the one preserved
Sedimentation; most organisms are preserved in this process as the organism buried in mud where some of the remaining are replaced by sulphide or phosphate mineral.
Recrystalisation; this method of preservation destroy microscopic details of the shell but does not change the overall shape, so it can keep morphological structure of the species.

All this methods of preservation helps to keep evidence of unknown species that live in the past which were influential to evolution as it buries the remaining bones of dead species.

Importance of fossils in evolution is that it helps researchers Archaeologist to identify species that live in the past decades and its origin; they can be used to interpret the process of evolution by using the fossilised material.

The fossil of different species can identify the indigenous species in the area, and they also play a part in tourist attraction because some of people would like to see the indigenous creature of the past. Fossils play a part in interpreting evolution because the remaining bones or shell support the findings of the researcher and what was happening in the previous years about different species that evolve.

Reference:

1. Fossilisation; [Internet] [cited 2006-May-04] Available from: http://www.musei.unina.it/Paleontologia/eng/3.2.4.1.htm.

2. Fossilisation; [internet] [cited 2006-May-03] Available from: http://www.museum.vic.gov.au/dinosaurs/sci-form.html.


Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://muanalo.blogspot.com

VARIATION IN SHELL STRUCTURE THAT OCCUR IN PHYLUM MOLUSCA

Malacology is the study of mollusks. There are about nine classes of mollusks where eight is still alive and one is discovered through fossilisation. Mollusks are defined generally as soft-bodied animal that usually produces exoskeleton. This external skeleton is called a shell. A shell is made up of calcium carbonate. The shell serves both for protection, decoration and supporting functions. The one feature common to all molluscs is the presence of a fleshy mantle. This is observed as a fold or lobe of fleshy material. It secretes, modifies and lines the shell. These animals need moisture to survive so they live in all parts of the world from deep water oceans to high upon the mountains. There are seven different classes of molluscs which are recognized (1).

The Gastropoda, this class is composed of 60,000 species. This is where we find species like Snail and Slugs. They have a well developed head with tentacles, often highly developed foot for crawling. “Shells can only be formed in fresh waters that are non-acidic, and in the ocean at depths above the level where the water becomes under saturated with Calcium Carbonate. Gastropods show different shapes, colours, patterns and sculpturing of their shell. In some gastropods, the shell is only conspicuously coiled in the early stages when it is still young. The coiling will disappear when the species grows and when it is an adult it will develop a single whorl shell which will be largely expanded. In many other gastropods, the shell has become more reduced or it is completely absent. In other cases the foot and mantle are very large and the mantle has reflexed backwards over the shell so that it becomes totally covered “ These animals are no longer able to pull their bodies completely into their shells (2).

The Bivalves comprise about 10,000 living species. “They have two valves made of calcium carbonate. Bivalves are mollusks in which the mantle cavity has been greatly enlarged in size, and whose gills, in addition to their respiratory function, act as a food sorting organ. The shell and mantle have become enlarged to cover the foot and mantle cavity completely. A clam shell consists of two halves or valves usually equal in size and shape, which are connected above by a flexible ligament whose resilience keeps them slightly open at the bottom. The valves of the shell can be shut by the contraction of one or two large muscles. The spring like ligament tends to hold the shell open, while the muscles enable the clam to shut its shell “ (3).

The Scaphopoda have about 350 living species. Tooth shells are occasionally called tusk shells; they are a member of the class Scaphopoda. The shell, which looks like a “miniature elephant tusk, is open at both ends. The narrow end often protrudes above the mud or sand in which the animal lives. Water currents enter a long mantle cavity that is lined with simple folds instead of gills. A combination of ciliary actions and muscular contractions of the foot circulates water and expels waste materials from the narrow end of the shell. Both head and foot can be extended from the broad end of the shell. The foot is modified to serve both in burrowing and feeding, it is used firrt to raise or lower the animal in the substrate to the point where food is available” (4).
The Chitons are often considered by scientists to be the most primitive of all existing molluscs. Strictly marine, the majority of the chiton species “inhabit rocky seashore environments where their low dome-shaped shells are well suited to withstanding the violent serge of ocean waves. They have a very broad creeping foot and a flattened visceral hump “ These organs are protected by an articulated shell of eight calcareous plates whose edges are formed by and embedded in a flexible part of the mantle called girdle (5).

The Aplacophora are about 250 described species, mostly found in deeper waters. “The class Aplacophora, animals also known as Solenogasters consists mostly of small worm-like molluscs that or feed upon the cnidarians. They have no shell, but have calcareous spicules in the body surface. The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body. Aplacophorans have a radula and a posterior mantle cavity”. Some are detritus feeders; others are predators (6).

The Cephalopoda have only about 400 species in existence now. “Only the tetrabranchs produce an external shell in this class of molluscs. Externally, the shell of the nautilus is creamy white with broad reddish-brown stripes. Inside it is brilliant, iridescent mother-of-pearl. The nautaloid shell is very complex, chambered and spiraled over the head of the animal. Even though coiled, it is radically different than that of the gastropods, being divided by transverse septa creating internal chambers”

The Monoplacophora are the “limpet-shaped molluscs which are segmented like worms. The internal vital organs are duplicated in each segment of this animal. They have a single, large, bilateral shell. The shell is a simple depressed limpet or disk -shaped valve, less than 25 millimetres across usually and is often thin and fragile (7).
Caudofoveata is the smallest class of molluscs. They are also called Chaetodermomorpha. They look like worms and they have no shells (8). Shells play a big role in our lives, apart from decorating our kitchens and our bath rooms they also serve as a symbol of hope.

Reference

1. Wikipedia contributors. Mollusca [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 24, 04:23 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Mollusca&oldid=54837475.

2. Wikipedia contributors. Gastropoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 23, 23:39 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Gastropoda&oldid=54800799

3. Wikipedia contributors. Bivalvia [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 12:59 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Bivalvia&oldid=51672364

4. Wikipedia contributors. Scaphopoda [Internet]. Wikipedia, The Free Encyclopaedia; 2006 May 04, 20:07 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Scaphopoda

5. Wikipedia contributors. Chiton [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 12, 14:07 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Chiton&oldid=52835758

6. Wikipedia contributors. Aplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 18, 05:55 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Aplacophora&oldid=53815532

7. Wikipedia contributors. Monoplacophora [Internet]. Wikipedia, The Free Encyclopaedia; 2006 April 22, 20:03 UTC [cited 2006 May 4]. Available from:
http://en.wikipedia.org/wiki/Monoplacophora

8. Wikipedia contributors. Caudofoveata [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 9, 09:07 UTC [cited 2006 May 24]. Available from: http://en.wikipedia.org/w/index.php?title=Caudofoveata&oldid=47675023.

Dianah Nangammbi
Cilla CSIR
P.O Box 395
Pretoria
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Cell: +27 73 121 3589
Email: dnangammbi@csir.co.za
http://wwwdianah.blogspot.com/